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Efficiently “pumping out” value-added resources from wastewater by bioelectrochemical systems: A review from energy perspectives

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Bioelectrochemical systems (BES) can accomplish simultaneous wastewater treatment and resource recovery via interactions between microbes and electrodes. Often deemed as “energy efficient” technologies, BES have not been well evaluated for their energy performance, such as energy production and consumption. In this work, we have conducted a concise review and analysis of energy balance in BES with parameters like normalized energy recovery, specific energy consumption, and net energy production. Several BES representatives based on their functions were selected for analysis, including direct electricity generation in microbial fuel cells, hydrogen production in microbial electrolysis cells, nitrogen recovery in BES, chemical production in microbial electrosynthesis cells, and desalination in microbial desalination cells. Energy performance was normalized to water volume (kWh m−3), organic removal (kWh kg COD−1), nitrogen recovery (kWh kg N−1), chemical production (kWh kg−1), or removed salt during desalination (kWh kg−1). The key operating factors such as pumping system (recirculation/feeding pumps) and external power supply were discussed for their effects on energy performance. This is an in-depth analysis of energy performance of various BES and expected to encourage more thinking, analysis, and presentation of energy data towards appropriate research and development of BES technology for resource recovery from wastewater.
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... However, the performance of the 3h HRT implies that more volume will be needed to produce the energy and proportionally less carbon will be removed per unit of wastewater volume. In terms of efficiency, the normalised energy recovery (NER) [42,43] is accepted as a good parameter to compare dissimilar bioelectrochemical systems that aim at converting organic substrate from wastewater into electricity. NER normalises the energy extracted either by the amount of COD removed (NER COD : KWh.Kg COD ...
... The longest HRT condition has the highest value (0.825 ± 0.086 KWh.m − 3 ; Fig. 7d), whilst the shorter HRT has the lowest value (0.143 ± 0.006 KWh.m − 3 ; Fig. 7d). Combined with the performance, these results suggest that the optimum balance between performance (Fig. 7c) and efficiency (Fig. 7d) [42]), but lower than the maximum (NER v = 1.35 KWh kg − 1 COD; [44]). Although not being an optimal feeding regime, the 65h HRT displayed a NER V twice higher (0.825 ± 0.086 KWh m − 3 ) than the maximum reported [44]. ...
... − 1 ). (d) Normalised energy recovery (NER) illustrating the energy conversion efficiency [42,43]. ...
Article
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Most advanced ceramic and self-stratifying microbial fuel cells designs were tested. • Ceramic microbial fuel cells have high energy conversion efficiency. • Ceramic microbial fuel cells have constant power performance. • Self-stratifying microbial fuel cells have constant energy conversion efficiency. • Self-stratifying microbial fuel cells have higher power performance at short HRT. A B S T R A C T In recent years, bioelectrochemical systems have advanced towards upscaling applications and tested during field trials, primarily for wastewater treatment. Amongst reported trials, two designs of urine-fed microbial fuel cells (MFCs) were tested successfully on a pilot scale as autonomous sanitation systems for decentralised area. These designs, known as ceramic MFCs (c-MFCs) and self-stratifying MFCs (s-MFC), have never been calibrated under similar conditions. Here, the most advanced versions of both designs were assembled and tested under similar feeding conditions. The performance and efficiency were evaluated under different hydraulic retention times (HRT), through chemical oxygen demand measures and polarisation experiments. Results show that c-MFCs displayed constant performance independently from the HRT (32.2 ± 3.9 W m − 3) whilst displaying high energy conversion efficiency at longer HRT (NER COD = 2.092 ± 0.119 KWh.Kg COD − 1 , at 24h HRT). The s-MFC showed a correlation between performance and HRT. The highest performance was reached under short HRT (69.7 ± 0.4 W m − 3 at 3h HRT), but the energy conversion efficiency was constant independently from the HRT (0.338 ± 0.029 KWh.Kg COD − 1). The c-MFCs and s-MFCs similarly showed the highest volumetric efficiency under long HRT (65h) with NER V of 0.747 ± 0.010 KWh.m − 3 and 0.825 ± 0.086 KWh.m − 3 , respectively. Overall, c-MFCs seems more appropriate for longer HRT and s-MFCs for shorter HRT.
... A wastewater-energy-chemical nexus can lead to a sustainable paradigm shift for the wastewater treatment industry, in which wastewater can be employed as a power source for energy production and chemical synthesis (Li et al., 2015;Lu et al., 2018;Mohan et al., 2016;Rabaey and Rozendal, 2010;Zou and He, 2018). When considering the large quantity of global wastewater (1,000 km 3 yr À1 ) (Heidrich et al., 2011), the large amount of chemical energy that it contains (17.8-28.7 kJ g À1 COD) is often overlooked (McCarty et al., 2011). ...
... Microbial electrochemical systems as a flexible platform technology involve the bioelectricity generation and utilization by electroactive microorganisms through the systems of microbial fuel cells (MFCs), microbial electrolysis cells, microbial electrosynthesis cells, and so on (Logan et al., 2019;Wang and Ren, 2013;Yan et al., 2013;Yong et al., 2014;Zou et al., 2016). Microbial electrosynthesis cells can provide comprehensive solutions for wastewater-energy-chemicals nexus by extracting the wastewater energy and efficiently converting it into various value-added chemicals (Harnisch and Schroder, 2010;Zou and He, 2018). In particular, the integration of microbial electrosynthesis cells with MFCs has accomplished the wastewater-powered production of different commodities, such as biomethane (Ning et al., 2021), acetic acid (Nevin et al., 2010), butanol (Zaybak et al., 2013), and hexanol (Vassilev et al., 2018), thereby opening the window for bringing value to wastewater treatment (Christodoulou et al., 2017;Jiang and Zeng, 2018). ...
... The ideal fitting of Nernst term means that the anodic current can reached 98% of the maximum value even a small overpotential of 100 mV is applied. The small U o and anodic overpotential indicate significantly reduced energy consumption compared with an OER anode (Zou and He, 2018). On the other hand, the current density of wastewater fed bioanode is much smaller than water splitting ($10 0 vs. 10 3 A m À2 ) (Yu et al., 2017), which might limit the product yield rate and increase the investment and maintenance cost of unit product. ...
Article
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A microbial electrochemical system could potentially be applied as a biosynthesis platform by extracting wastewater energy while converting it to value-added chemicals. However, the unfavorable thermodynamics and sluggish kinetics of in vivo whole-cell cathodic catalysis in a microbial electrochemical system largely limit product diversity and value. Herein, we convert the cathodic reaction from in vivo whole-cell catalysis to in vitro enzymatic catalysis and develop a microbe-enzyme hybrid bioelectrochemical system (BES), where microbes release the electricity in wastewater (anode) to power enzymatic catalysis (cathode). Three different examples for the synthesis of pharmaceutically relevant compounds, including halofunctionalized oleic acid (HOA) based on a cascade reaction, (4-chlorophenyl)-(pyridin-2-yl)-methanol (CPMA) based on electrochemical cofactor regeneration, and l-3,4-dihydroxyphenylalanine (L-DOPA) based on electrochemical reduction demonstrate that the hybrid BES design not only overcomes the thermodynamic and kinetic limitations of the cathode but also accomplishes the wastewater-powered production of high-value chemicals instead of low-value commodities. According to the techno-economic analysis, this system could deliver high system profit, opening an avenue to a potentially viable wastewater-to-profit process while shedding scientific light on hybrid BES mechanisms toward a sustainable reuse of wastewater.
... The use of air-cathode MFCs (ACMFCs) can avoid the need for auxiliary equipment on the cathodes and synchronously remove carbon and nitrogen. Thus, these cathodes promote simpler and more cost-effective operation of MFCs (Cheng and Logan, 2011;Estrada-Arriaga et al., 2017;Wang et al., 2017;Yang et al., 2018bYang et al., , 2019Zou and He, 2018). ACMFCs hold great practical value in wastewater treatment applications, including power recovery (Ieropoulos et al., 2010;Liu and Logan, 2004), pollutant removal (Feng et al., 2008;Park et al., 2017;Puig et al., 2011;Yan et al., 2012;Z. ...
... Many approaches have been developed to enable the application of ACMFCs to sustainable wastewater treatment; the approaches generally include tailoring of the electrode materials and catalysts (Zou and He, 2018), electrode spacing (Moon et al., 2015;Park et al., 2018), external resistance (R ext ) (Ghadge and Ghangrekar, 2015;Jung and Regan, 2011), solution conductivity or buffer (Rossi et al., 2017), and initial substrate concentration (Huang et al., 2018;Mahmoudi et al., 2020). The composition and concentration of substrate is known to affect the performance of MFCs critically. ...
... The normalized energy recovery (NER) was quantified by normalizing the power production (P) per kilogram of COD (NER COD , kWh kg −1 COD) or per cubic meter (NER V , kWh m −3 ) using Eqs. (9) and (10) Xiao et al., 2014;Zou and He, 2018). Independent triplicate experiments were run for each stability test. ...
Article
Air-cathode microbial fuel cells (ACMFCs) can extract available electrons from the low C/N ratio wastewater (LCNW) for pollutant degradation and power generation. However, the multiple effects of operating parameters and their relationship between the performances and parameters are still lacking. In this study, several ACMFCs for simultaneous nitritation/denitritation (SND) and energy recovery were constructed and evaluated in terms of chemical oxygen demand (COD), NH4⁺-N, C/N ratio, phosphate buffer solution (PBS), and external resistance (Rext), and several derived parameters (e.g., organic loading rate (OLR), nitrogen loading rate (NLR)). Results indicated that ACMFCs could be used to treat LCNW successfully with high pollutant removal rates and sustainable current generation. Maximum removal efficiencies of 94% COD, 92% NH4⁺-N, and 92% total nitrogen (TN) were achieved. A maximum power density of 1400 mW m⁻² and columbic efficiency of 69.2% were also obtained at a low C/N ratio of 1.7–2.6. Low C/N ratios promoted SND by balancing nitritation and denitritation. The microbial community and their predicated function results showed considerable nitrifiers and denitrificans were enriched in the ACMFCs, contributing to SND and power recovery. Further analyses showed that the NH4⁺-N could inhibit SND, but PBS and Rext had no obvious effects on this outcome. Co-occurrence network analysis demonstrated that power is positively correlated with COD and Rext; strong correlations between organic removal and COD, and between nitrogen removal and ammonia, conductivity, and C/N ratio were also noted. Overall, the appropriate control of such parameters is necessary to achieve efficient SND in ACMFCs for LCNW treatment.
... As Xiao et al. (2014) explored, NER correlates the inflow rate and organic matter removal without considering the influence of reactor dimensions, which consider it more suitable for upscaling applications . Earlier NER analysis of MFC could reach a maximum value of 2.2 kWh/m 3 and 2 kWh/kg⋅COD, independent of reactor size (Wen et al., 2010;Tugtas et al., 2011;Zou and He, 2018). Term NER represents size doesn't serve as a restrictive factor for estimating the energy recovery of the system (Bird et al., 2022). ...
... The main goal of the present review is to provide deep insights and views on system optimization with a realistic picture of energy-efficient/ sustainable energy and valuable resources recovery in BES. Such efforts will be helpful to promote more logical thinking, investigation, and expression of energy balance data for future generations of BES researchers before attempting the scaling-up trials (Zou and He, 2018). Additionally, it is high time to standardize the performance indices to assess the performance of BES and make one single frame for standardization of methods for operations, which can be a meaningful tool for accurate data comparison while moving toward commercialization of microbial electrochemical technologies (Jadhav et al., 2021a,b). ...
Article
Electrochemists and ecological engineers find environmental bioelectrochemistry appealing; however, there is a big gap between expectations and actual progress in bioelectrochemical system (BES). Implementing such technology opens new opportunities for novel electrochemical reactions for resource recovery and effective wastewater treatment. Loopholes of BES exist in its scaling-up applications, and numerous attempts toward practical applications (200, 1000, and 1500 L) are key successive indicators toward its commercialization. This review emphasized the critical rethinking of standardization of performance indices i.e. current generation (A/m²), net energy recovery (kWh/kg·COD), product yield (mM), and economic feasibility ($/kWh) to make fair comparison with the existing treatment system. Therefore, directional perspectives, including modularity, energy-cost balance, energy and resource recovery, have been proposed for the sustainable market of BES. The current state of the art and up-gradation in resource recovery and contaminant removal warrants a systematic rethinking of functional worth and niches of BES for practical applications.
... One of the most known types of MES is the microbial fuel cell (MFC). Other types of microbial electrolysis cells (MES) include microbial electrolysis cells (MEC), microbial electrosynthesis system (MES), and microbial desalination cells (MDC) (Fig. 12) (Zou and He, 2018). MFC is an electrochemical cell that uses microorganisms as a catalyst for the oxidation of organic matter and consequently the production of electricity. ...
... Diagrams of microbial fuel cell (MFC), microbial electrolysis cell (MEC), microbial electrosynthesis system (MES), and microbial desalination cell (MDC)(Zou and He, 2018). ...
Chapter
Clean water is a key factor to sustain life on earth. Nevertheless, it is challenging to provide clean water at a sufficient rate that will fulfill the growing demand. This is due to the continued increase of the world population and scarcity of clean water sources. However, for every problem, there is a solution; therefore, clean water can be regenerated from wastewater through different treatment mechanisms. Those mechanisms can be classified as either physical, chemical, or biological. Wastewater treatment plants consist of different stages starting from the preliminary stage to the secondary stage. The physical and chemical treatments precede the secondary treatment. The focus of this chapter will be on the secondary stage of wastewater treatment, whereby different microorganisms are used in wastewater treatment. This falls under the biological treatment category. Microorganisms clean wastewater by breaking down various pollutants, more specifically, organic matter. Microbes are used to facilitate the degradation of the organic content including, but not limited to, fungi, protozoa, algae, and bacteria, which can function under aerobic and/or anaerobic conditions. Moreover, wastewater treatment using the microbial community can take various forms such as using microbial electrolysis cell (MEC) or microbial fuel cell (MFC). The efficiency of the treatment process is affected by various factors such as temperature, pH, and types of microbes.
... Other parameters, for example, power density or conversion efficiency are often used as a relative method of showing improvement. Further to that, it was proposed by He that assessment based on building an energy balance is a necessary step to comprehend energy issues (He, 2013;He, 2017), providing valuable information to optimise MFC operation, which in turn encourages more thinking, analysis, and presentation of energy data (Zou and He, 2018). Indeed, when reporting power-densities alone, this can be insufficient to illustrate the true potential of a design as an implementable solution for a practical application. ...
... Hence, in terms of practical implementation, normalisation by the geometric volume of the reactor should be preferred. This is why having a parameter that combines both aspects (volume and power) is of interest to compare the overall efficiency of a proposed solution, such as the Normalised Energy Recovery (NER) proposed by He et al.: The presentation of scaled-up systems operating in real applications gives invaluable means of energy recovery (measurable and/or usable) and one true metric of value as the real operation and benefits can be assessed both by operators (researchers, scientific community) as well as the general public (He, 2013;He, 2017;Zou and He, 2018). Whilst the number of decentralised urinepowered systems is increasing, techno-economic analysis shows MFC systems as a contender technology for wastewater treatment (Jadhav et al., 2021). ...
Chapter
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Although first presented by M.C. Potter in 1911, bioelectrochemical systems have essentially only received increased attention in the last 30 years. This is primarily due to the technology’s multi-functional properties such as generating electrical current, producing hydrogen gas, enabling the recycling of nutrients, mineralising organic matter, or killing pathogens. In a world facing the urgent need for developing a sustainable society, such technology appears as an essential element of a diversified biotechnological portfolio. Research has primarily focused on developing bioelectrochemical systems that strike a fine balance between all the applications this technology can offer. However, only a few of these aspects have been sufficiently developed to reach pilot-scale testing. This chapter will focus on the implementation of bioelectrochemical systems that have reached the stage of pilot-scale trials.
... MFCs are a type of BES that uses EAM to generate bioelectricity by oxidizing a wide range of biomass and organic waste as a potential substrate (Chandrasekhar et al., 2021c;Wilberforce et al., 2021;Wu et al., 2021). The chemical energy present in the wastewater will be extracted and effectively biotransformed into a variety of value-added chemicals using BESC's complete wastewater-energy-chemicals solutions (Nancharaiah et al., 2016;Zou and He, 2018). Because of the combination of BESC and MFCs, it is now possible to produce a variety of valuable products from wastewater (Gambino et al., 2021;Mohan and Chandrasekhar, 2011), including biomethane (Ning et al., 2021), ethanol, acetate, propionate, butyrate , butanol (Zaybak et al., 2013), and hexanol (Vassilev et al., 2018), and hydrogen gas (Kadier et al., 2015). ...
... Even though BES is supposedly "energy-efficient," it must be assessed on an energy scale to explain its economic viability against other wastewater resource recovery techniques to determine specific usage niches that guide BES research and innovation. The potential benefits of the BES technique will be found in the fact that it requires minimal energy to operate and recovers the greatest quantity of energy and other value-added resources, which include nutrients and/or high-quality recyclable water (Zou and He, 2018). According to research findings on BESC, the installation of extra "pin" electrodes may allow for in situ electrode potential modification and control. ...
Article
Bioelectrochemical systems (BES) have the potential to be used in a variety of applications such as waste biorefinery, pollutants removal, CO2 capture, and the electrosynthesis of clean and renewable biofuels or byproducts, among others. In contrast, many technical challenges need to be addressed before BES can be scaled up and put into real-world applications. Utilizing BES, this review article presents a state-of-the-art overall view of crucial concepts and the most recent innovative results and achievements acquired from the BES system. Special attention is placed on a hybrid approach for product recovery and wastewater treatment. There is also a comprehensive overview of waste biorefinery designs that are included. In conclusion, the significant obstacles and technical concerns found throughout the BES studies are discussed, and suggestions and future requirements for the virtual usage of the BES concept in actual waste treatment are outlined.
... In BES, active microorganisms transfer ions between electrodes and stimulate denitrification at the cathode compartment . BES is available in two types: microbial fuel cell (MFC) and microbial electrolysis cell (MEC), both of them are working based on living microorganisms (Zou & He 2018). For NH 4 -N and P recovery from the RW, MFC was considered due to its negative energy balance (Kuntke et al. 2018;Zou & He 2018). ...
... BES is available in two types: microbial fuel cell (MFC) and microbial electrolysis cell (MEC), both of them are working based on living microorganisms (Zou & He 2018). For NH 4 -N and P recovery from the RW, MFC was considered due to its negative energy balance (Kuntke et al. 2018;Zou & He 2018). In other words, within MFCs electricity generation takes place simultaneously with the NH 4 -N and P recovery (Kuntke et al. 2012;Rodríguez Arredondo et al. 2015). ...
Article
Full-text available
Wastewater treatment plants (WWTP) have extensive energy processes that undermine their economic and environmental performance. In this context, the integration of wastewater treatment with other biochemical processes such as co-digestion of sludge with organic wastes, and production of value-added products at their downstream processes will shift conventional WWTPs into biorefinery platforms with better sustainability performance. The sustainability of such a biorefinery platform has been investigated herein using an economic and life cycle assessment approach. This WWTP-based biorefinery treats wastewater from Copenhagen municipality, co-digests the source-sorted organic fraction of municipal solid waste and sludge, and upgrades biogas into biomethane using a hydrogen-assisted upgrading method. Apart from bioenergy, this biorefinery also produces microbial protein (MP) using recovered nutrients from WWTP's reject water. The net environmental savings achieved in two damage categories, i.e., −1.07 × 10−2 species.yr/FU in ecosystem quality and −1.68 × 106 USD/FU in resource scarcity damage categories along with high potential windows for the further environmental profile improvements make this biorefinery platform so encouraging. Despite being promising in terms of environmental performance, the high capital expenditure and low gross profit have undermined the economic performance of the proposed biorefinery. Technological improvements, process optimization, and encouraging incentives/subsidies are still needed to make this platform economically feasible. HIGHLIGHTS A biorefinery for microbial protein and bioenergy production has been developed.; Wastewater treatment and anaerobic digestion of sludge incorporated in biorefinery.; Microbial production had lower environmental profile than soybean meal.; High CAPEX undermined the economic feasibility of MP production.;
... External power applied onto the electrical circuit of BES drives electrons from anode to the cathode and also supports the hydrogen generation at the cathode (Wang and Ren, 2013;Santoro et al., 2017). In contrast to MFC, the cathode of MEC works in anaerobic conditions to allow the production of hydrogen (Zou and He, 2018). However, the anaerobic conditions of the MEC´s cathode can also promote the production of methane, once CO 2 and methanogens are available. ...
... Microbial electrosynthesis (MES), also known as bioelectrosynthesis, is another variant of BES, which utilizes the reducing power generated from the anodic oxidation to produce high value-added products in the cathode. The microorganisms present in the cathode that are commonly present as a microbial biofilm attached to the cathode's surface are responsible for reducing the available terminal electron acceptor to produce high value-added products, such as acetate, ethanol, and butyrate (Bajracharya et al., 2016;Zou and He, 2018). As described by Bajracharya et al. (2017a), the bioelectrosynthesis of diverse chemical compounds is driven by CO 2 reduction as well as reduction/oxidation of other organic feedstocks using microbes as biocatalysts. ...
... Therefore, the total amount of recovered NH 4 -N was 83.62 t/year, and its concentration was 219.50 mg/L. Microbial fuel cells (MFCs) have a negative energy balance (explained in supplementary file SI-9), so the amount of energy consumed in the bioelectrochemical system was considered to be zero [41,42]. ...
... Even though the equipment used in MFCs (feed pumps and recirculation pump) consumes electricity, MFCs have a negative energy balance. According to the literature, net electricity saving for MFCs ranges between − 0.8 and − 8.5 kWh/kg N [41,43]. The electricity production by BES was estimated at 389 MWh. ...
Article
The growing population and the consequent protein scarcity have led to innovation in proteinaceous feed production methods. In this regard, the upcycling of nitrogen rich effluents into microbial protein (MP)/single cell protein (SCP) is considered as an innovative solution. This paper aims to employ life cycle assessment to identify the most environmentally friendly strategy to upcycle nitrogen (N) and carbon (C) flows from wastewater treatment plant (WWTP) into MP. Accordingly, several pathways for integrating WWTP and MP production facility were evaluated, in terms of C source (i.e., biogas or biomethane) and the pretreatment method applied to the reject water (RW) (i.e., centrifugation + filtration + pasteurization, electrochemical extraction, bio-electrochemical extraction). The results indicated that electrochemical and bio-electrochemical N recovery not only safely extracted N from RW but also led to promising solution for MP production from WWTP effluents. The pathway including bio-electrochemical N recovery and use of biologically upgraded biomethane for MP had 42.17%, 195.95%, and 172.03% better environmental performance regarding human health, ecosystem quality, and resource scarcity, respectively, compared with standalone WWTP without MP production. However, the electrochemical N recovery outperformed other scenarios in the human health with a net impact of 2.72 DALY/FU and ‎in ecosystem quality damage categories with a saving of -0.033 ‎Species/FU. The results reported herein indicated that the use of chemical nutrients to enrich the cultivation medium had significant impacts on the overall environmental performance of the suggested biorefinery. Decreasing the consumption of synthetic nutrients and improving N to protein conversion efficiency by 20% can make the established pathway much more competitive with conventional proteinaceous feed sources such as soybean meal.
... The electrons in the anolyte [31] are transferred extracellularly [27,40,41] to the anode [42] where the electric energy starts to incur [30] with the electrode potential difference in the presence of the applied voltage [40]. The electrons travel directly via the external circuit of the cell to the cathode [4,26,43] and are facilitated by the electroactive bacteria [28,40,44]. The mechanism of the electron transfer, either by an endogenous mediator (intercellular and extracellular) or a direct contact [44], is highly dependent on the microorganisms present in the anodic chamber [45]. ...
... The mechanism of the electron transfer, either by an endogenous mediator (intercellular and extracellular) or a direct contact [44], is highly dependent on the microorganisms present in the anodic chamber [45]. Meanwhile, free protons or hydrogen ions in the anolyte [42] pass across the membrane to reach the catholyte [5,11,12,14,31] before being electrically reduced [11,12,36] into biohydrogen in the cathodic chamber [31,43] as a result of accepting the electrons at the cathode surface [5,38,39] with the supply of the required low external voltage [27,30]. ...
Article
Microbial electrolysis cell (MEC) is a promising reactor. However, currently, the reactor cannot be adapted for industrial-scale biohydrogen production. Nevertheless, this drawback can be overcome by modeling studies based on mathematical equations. The limitation of analytical instrumentation to record the non-linearity of the dynamic behavior for biohydrogen processes in an MEC has led to the introduction of computational approach that has the potential to reduce time constraints and optimize experimental costs. Reviews of comparative studies on bioelectrochemical models are widely reported, but there is less emphasis on the MEC model. Therefore, in this paper, a comprehensive review of the MEC mathematical model will be further discussed. The classification of the model with respect to the assumptions, model improvement, and extensive studies based on the model application will be critically analyzed to establish a methodology algorithm flow chart as a guideline for future implementation.
... Bioelectrochemical systems, such as microbial fuel cells, have been widely researched because they can treat wastewater and generate electricity, hydrogen, or valuable chemical compounds simultaneously (Zou & He 2018). Microbial fuel cells can achieve up to 90% removal of chemical oxygen demand (COD) (Tsekouras et al. 2022), making them similar to conventional activated sludge treatment technologies (Christian et al. 2008). ...
Article
Full-text available
Research regarding microbial fuel cells has been stimulated to reduce the operating costs and energy consumption of conventional wastewater treatment, and increase its profitability. However, these devices are challenging to study due to their complexity and sensitivity to both internal and external factors. Artificial intelligence (AI) has been used to analyze microbial fuel cells as an effective alternative to the use of mathematical models, which are still in development. In this study, the main goals were to perform the first bibliometric analysis of AI applied to microbial fuel cell research and to find the most popular algorithms used to date. Using the Web of Science database, a total of 102 articles published between 1999 and 2022 were retrieved. The cumulative number of articles has greatly increased over the past 10 years. About 55% were contributed by researchers from China and USA, leading among 20 countries. Some 50 algorithms were used, with principal component analysis and feed-forward neural networks being the most popular used to study and optimize microbial fuel cells. HIGHLIGHTS The first bibliometric analysis of applied to microbial fuel cell research was performed.; The number of publications has grown exponentially since 2013.; 102 articles were published between 1999 and 2022.; 50 AI algorithms have been used in microbial fuel cell research.; The most popular algorithms are principal component analysis and feed-forward neural networks.;
... High purity struvite is precipitated from solutions after regeneration of ion exchangers [87]. Anaerobic membrane bioreactors [88], ion exchange and adsorption, magnetic microsorbents, reactive filtration, electrodialysis, biochemical and electrochemical systems [89,90], forward osmosis [91] or Integrated Constructed Wetlands (ICW) [92] were also investigated [88,89,91,[93][94][95]. ...
Article
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Phosphorus is one of the most important macronutrients needed for the growth of plants. The fertilizer production market uses 80% of natural, non-renewable phosphorus resources in the form of phosphate rock. The depletion of those deposits forces a search for other alternatives, including biological waste. This review aims to indicate the most important ways to recover phosphorus from biowaste, with particular emphasis on wastewater, sewage sludge, manure, slaughter or food waste. A comparison of utilized methods and directions for future research based on the latest research is presented. Combining biological, chemical, and physical methods with thermal treatment appears to be the most effective way for the treatment of wastewater sludge in terms of phosphorus recovery. Hydrothermal, thermochemical, and adsorption on thermally treated adsorbents are characterized by a high phosphorus recovery rate (over 95%). For animal by-products and other biological waste, chemical methods seems to be the most optimal solution with a recovery rate over 96%. Due to its large volume and relatively low phosphorus content, wastewater is a resource that requires additional treatment to recover the highest possible amount of phosphorus. Pretreatment of wastewater with combined methods seems to be a possible way to improve phosphorus recovery. A compressive evaluation of combined methods is crucial for future research in this area.
... Microbial electrochemical technology (MET) is a platform technology in which electroactive microorganisms are used to catalyze bioelectrochemical reactions to generate energy and products from waste carbon materials (Wang & Ren, 2013;Zou & He, 2018). In this process, oxidation and reduction reactions are separated in suitable environmental conditions for the first time. ...
Chapter
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The water sector is in the middle of a paradigm shift from focusing on treatment and meeting discharge permit limits to integrated operation that also enables a circular water economy via water reuse, resource recovery, and system level planning and operation. While the sector has gone through different stages of such revolution, from improving energy efficiency to recovering renewable energy and resources, when it comes to the next step of achieving carbon neutrality or negative emission, it falls behind other infrastructure sectors such as energy and transportation. The water sector carries tremendous potential to decarbonize, from technological advancements, to operational optimization, to policy and behavioural changes. This book aims to fill an important gap for different stakeholders to gain knowledge and skills in this area and equip the water community to further decarbonize the industry and build a carbon-free society and economy. The book goes beyond technology overviews, rather it aims to provide a system level blueprint for decarbonization. It can be a reference book and textbook for graduate students, researchers, practitioners, consultants and policy makers, and it will provide practical guidance for stakeholders to analyse and implement decarbonization measures in their professions. ISBN: 9781789061789 (Paperback) ISBN: 9781789061796 (eBook) ISBN: 9781789061802 (ePUB)
... Microbial electrochemical technology (MET) is a platform technology in which electroactive microorganisms are used to catalyze bioelectrochemical reactions to generate energy and products from waste carbon materials (Wang & Ren, 2013;Zou & He, 2018). In this process, oxidation and reduction reactions are separated in suitable environmental conditions for the first time. ...
Chapter
Full-text available
The water sector is in the middle of a paradigm shift from focusing on treatment and meeting discharge permit limits to integrated operation that also enables a circular water economy via water reuse, resource recovery, and system level planning and operation. While the sector has gone through different stages of such revolution, from improving energy efficiency to recovering renewable energy and resources, when it comes to the next step of achieving carbon neutrality or negative emission, it falls behind other infrastructure sectors such as energy and transportation. The water sector carries tremendous potential to decarbonize, from technological advancements, to operational optimization, to policy and behavioural changes. This book aims to fill an important gap for different stakeholders to gain knowledge and skills in this area and equip the water community to further decarbonize the industry and build a carbon-free society and economy. The book goes beyond technology overviews, rather it aims to provide a system level blueprint for decarbonization. It can be a reference book and textbook for graduate students, researchers, practitioners, consultants and policy makers, and it will provide practical guidance for stakeholders to analyse and implement decarbonization measures in their professions. ISBN: 9781789061789 (Paperback) ISBN: 9781789061796 (eBook) ISBN: 9781789061802 (ePUB)
... Most research studies reported direct energy/electricity production in W.m −2 or W.m −3 (as power density) but not as energy performance with an actual unit of Joule or kilowatt-hour. Currently, few studies focus on energy performance studies in terms of normalized energy recovery (NER), specific energy consumption (SEC), and net energy production (NEP) (Zou and He 2018). ...
Article
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The world faces tremendous challenges and environmental crises due to the rising strength of wastewater. The conventional technologies fail to achieve the quality water that can be reused after treatment means “zero effluent” discharge of the industrial effluent. Therefore, now the key challenge is to develop improved technologies which will have no contribution to secondary pollution and at the same time more efficient for the socio-economic growth of the environment. Sustainable technologies are needed for wastewater treatment, reducing footprint by recycling, reusing, and recovering resources. Advanced oxidation process (AOP) is one of the sustainable emerging technologies for treating refractory organic contaminants present in different industrial wastewaters like textile, paper and pulp, pharmaceuticals, petrochemicals, and refineries. This critical review emerges details of advanced oxidation processes (AOPs), mentioning all possible permutations and combinations of components like ozone, UV, the catalyst used in the process. Non-conventional AOP systems, microwave, ultrasound, and plasma pulse assisted are the future of the oxidation process. This review aims to enlighten the role of AOPs for the mineralization of refractory organic contaminants (ROC) to readily biodegradable organics that cannot be either possible by conventional treatment. The integrated AOPs can improve the biodegradability of recalcitrant organic compounds and reduce the toxicity of wastewater, making them suitable for further biological treatment. Graphical abstract
... The key power consumption in the entire process are pumping system (feeding pumps/ recirculation) and external power source in the case of MEC. The analysis shows the comparison with various studies that the energy balance is positive due to the higher value of produced hydrogen and chemicals during the process (Zou and He 2018). The microbial desalination cell (MDC) shows better performance with applied external potential and lower total energy consumption (Sevda et al. 2015, Sevda and Abu-Reesh 2017a, b, 2018. ...
Book
Extensive use of fossil fuels for energy have negatively contributed to the environment owing to the emission of carbon dioxide and other harmful gases as serious atmospheric pollutants and particulates, and has resulted in soaring global warming. At the same time, various waste products from domestic, agricultural, animal facilities, refieries and industries also cause a tremendous environmental burden that needs treatment and recycle. Energy systems from MFC’s can be used for combating both environmental problems and offsetting the pollution loads. This creates more opportunities for renewable and green fuel production that can substitute fossil fuels and generate commercially important coproducts from waste substrates. MFC’s has a plethora of benefis, over other kinds of energy production routes with a) ceased emissions (such as SOx, NOx, CO2 and CO), b) higher effiiency, c) no mobile parts and d) least sound pollution. Although there have been signifiant attempts to produce bioelectricity from bacterial electrolytic systems right from early 1900’s, there were limitations in the yield and feasibility of the process. However, early 1990’s witnessed innovations in MFC designs and incorporation of various electron donor, electrode apparatus and biocatalysts (biological agents: algae etc.) and thus have become far more appealing. This book will focus on the state of the art of MFC’s with various combinatories of substrates yielding bioelectricity with valued co-products. Essentially the book will provide fundamental ideas and basics of MFC technologies, entailing various design and modelling aspects with examples. Various sections of the book will deal with unique aspects of basic sciences, reactor confiuration, application, market feasibility with lucid illustrations and explanations.
... Usually, at least one of the exoelectrogens and electrotrophs is involved in the system as a bioanode and biocathode, respectively, to facilitate electron transport. The exoeletrogens are EAM that donate electrons to the anodic electrode, while the eletrotrophs are EAM that capture electrons from the cathodic electrode [33]. Direct electron transfer (DET) and indirect electron transfer (IET) are two major electron transfer patterns between microorganisms and electrodes [34,35]. ...
Article
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Bioelectrochemical system (BES) is an emerging technology for wastewater treatment. The urgent requirement for dealing with water shortage, wastewater treatment and reuse, energy generation, and resources recovery has promoted intensive research in BES during the last decade. This review summarizes the latest typical BES configurations based on specific functions, including microbial fuel cells (MFC), microbial electrolysis cells (MEC), microbial electrosynthesis systems (MSS), microbial desalination cells (MDC), microbial recycling cells (MRC), microbial solar cells (MSC), and microbial electrochemical snorkel (MES). The removal of contaminants, particularly emerging organic, non-metallic, metallic, and metalloid contaminants, and the recovery of resources in the form of bioenergy, biofuel, nutrients, metals, and metalloids in wastewater treatment using BES technology have been reviewed in this work. Limitations of BES technology in terms of reactor performance, scale-up, and construction costs for real-world wastewater treatment applications are discussed and future research directions needed for the successful deployment of BES technology are proposed.
... Net energy production (NEP) is calculated by subtracting process energy consumption from NER. The energy consumption was mainly due to the pumps for feeding (both feeding and recirculation), external aeration or light illumination, or power supply (Zou and He, 2018). The three MFC reactors have different energy consumption, from which the MFC-AS can use continuous aeration, while the MFC-IFAS and MFC-IFAS/MA can use intermittent aeration and illumination respectively. ...
Article
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The sustainability and innovation of a novel leachate treatment technology is a matter of vital significance. Bio-electrochemical-driven wastewater and leachate treatment methods, particularly MFC, and their improvements have attracted scientists’ attention recently. This study developed a new MFC system, which consisted of an anodic chamber, a cathode chamber with fixed biofilm carriers and a low-cost sheet of carbon felt between them as a membrane-like separator. The study was conducted to evaluate the capacity of MFC coupled with integrated fixed-film activated sludge (IFAS), to enhance the efficiency of the treatment and the amount of energy produced. Three MFC systems with different cathode processes were compared, namely, conventional activated sludge (MFC-AS), MFC-IFAS, and microalgae coupled MFC-IFAS (MFC-IFAS/MA). The experimental results revealed that MFC-IFAS/MA produced higher power density and nitrogen removal than the other two systems. The average removals of COD, NH4⁺-N, and total nitrogen (TN) were, 69.9%, 84.2% and 60.5% for MFC-AS, 84.3%, 79.2% and 71.6% for MFC-IFAS; and 82.0%, 90.3% and 88.6% for MFC-IFAS/MA. MFC-IFAS/MA demonstrated its superior electrochemical behaviors and nitrogen removal and this behavior was referring to the dual effect of fixed-biofilm and microalgae assimilation. This study investigated for the first time the symbiosis between microalgae and IFAS in an MFC reactor, which may open a new prospect for MFC application.
... It is thus important to supplement an electron donor with lower electrode potential and thus boost the overall potential difference of SWEFC. The application of various substrates such as acetate, glucose, and lactate as electron donors for the treatment of domestic and industrial wastewater in bioelectrochemical systems (BES) has been extensively reported (Zhou and He 2018). Substrate utilization plays a pivotal role in any biological process, as it primarily represents the carbon and energy sources for the microorganisms. ...
Article
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A novel tubular sediment–water electrolytic fuel cell (SWEFC) was fabricated for the reduction of Cr(VI) in a dual-phase system. The approach simulates a standing water body with Cr(VI)-contaminated overlying water (electrolyte) and bottom sediment phase with electrodes placed in both the phases, supplemented with urea as a potential electron donor. Cr(VI) reduction efficiency of 93.2 ± 1.3% from electrolyte (in 1.5 h) and 81.2 ± 1.3% from the sediment phase (in 8 h) with an initial Cr(VI) concentration of 1,000 mg/L was observed in a single-cell configuration. The effect of initial Cr(VI) concentration, variation in sediment salinity and pH, and different electron donors on the SWEFC performance were systematically investigated. SWEFC showed enhanced performance with 2.4-fold higher current (193.9 mA) at 400 mg/L Cr(VI) concentration when cow dung was used as a low-cost alternative to urea as an electron donor. Furthermore, reactor scalability studies were carried out with nine-anode and nine-cathode configuration (3 L electrolyte and 2 kg sediment), and reduction efficiencies of 98.9 ± 0.9% (in 1 h) and 97.6 ± 2.2% (in 8 h) were observed from the electrolyte and sediment phases, respectively. The proposed sediment–water electrolytic fuel cell can be an advanced and environmentally benign strategy for Cr(VI) remediation from contaminated sediment–water interfaces along with electricity generation. Graphical abstract
... The main energy consumers considered were: (i) pumping system for feeding and recirculation in both reactors and (ii) external power supply. The energy consumption of pumps for each subunit was calculated as proposed by (Zou and He, 2018) (Supplementary data, Energy calculation). Finally, the construction cost (CAPEX) was estimated, assuming the electrodes and the membranes as the main cost. ...
Article
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Electro bioremediation is gaining interest as a sustainable treatment for contaminated groundwater. Nevertheless, the investigation is still at the laboratory level, and before their implementation is necessary to overcome important drawbacks. A prevalent issue is the high groundwater hardness that generates scale deposition on electrodes that irreversibly affects the treatment effectiveness and their lifetime. For this reason, the present study evaluated a novel and sustainable approach combining electrochemical water softening as a preliminary step for electro bioremediation of nitrate-contaminated groundwater. Batch mode tests were performed at mL-scale to determine the optimum reactor configuration (single- or two-chambers) and the suitable applied cathode potential for electrochemical softening. A single-chamber reactor working at a cathode potential of -1.2 V vs. Ag/AgCl was chosen. Continuous groundwater softening under this configuration achieved a hardness removal efficiency of 64 ± 4% at a rate of 305 ± 17 mg CaCO3 m-2cathode h-1. The saturation index at the effluent of the main minerals susceptible to precipitate (aragonite, calcite, and brucite) was reduced up to 90%. Softening activity plummeted after 13 days of operation due to precipitate deposition (mostly calcite) on the cathode surface. Polarity reversal periods were considered to detach the precipitated throughout the continuous operation. Their implementation every 3-4 days increased the softening lifetime by 48%, keeping a stable hardness removal efficiency. The nitrate content of softened groundwater was removed in an electro bioremediation system at a rate of 1269 ± 30 g NO3- m-3NCC d-1 (97% nitrate removal efficiency). The energy consumption of the integrated system (1.4 kWh m-3treated) confirmed the competitiveness of the combined treatment and paves the ground for scaling up the process.
... Geobacter and Shewanella have been extensively studied for their functional roles in terrestrial and marine subsurface, whose anoxic environments are deficient in soluble electron acceptors. The unique metabolism of such bacteria has been applied in bioelectrochemical systems (BESs) to be used for wastewater treatment [1], production of renewable energy and value-added products [2], and bioremediation [3]. Both culture-dependent and -independent studies have revealed the presence and functional role of electrogenic microbes other than Geobacter and Shewanella [4]. ...
... Geobacter and Shewanella have been extensively studied for their functional roles in terrestrial and marine subsurface, whose anoxic environments are deficient in soluble electron acceptors. The unique metabolism of such bacteria has been applied in bioelectrochemical systems (BESs) to be used for wastewater treatment [1], production of renewable energy and value-added products [2], and bioremediation [3]. Both culture-dependent and -independent studies have revealed the presence and functional role of electrogenic microbes other than Geobacter and Shewanella [4]. ...
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In this study, a novel electrogenic bacterium denoted as strain NIT-T3 of the genus Desulfuromonas was isolated from a graphene-oxide-reducing enrichment culture that was originally obtained from a mixture of seawater and coastal sand. Strain NIT-T3 utilized hydrogen and various organic acids as electron donors and exhibited respiration using electrodes, ferric iron, nitrate, and elemental sulfur. The strain contained C16:1ω7c, C16:0, and C15:0 as major fatty acids and MK-8, 9, and 7 as the major respiratory quinones. Strain NIT-T3 contained four 16S rRNA genes and showed 95.7% similarity to Desulfuromonasmichiganensis BB1T, the closest relative. The genome was 4.7 Mbp in size and encoded 76 putative c-type cytochromes, which included 6 unique c-type cytochromes (<40% identity) compared to those in the database. Based on the physiological and genetic uniqueness, and wide metabolic capability, strain NIT-T3 is proposed as a type strain of ‘Desulfuromonas versatilis’ sp. nov.
... Platform technology for novel applications (Butti et al. 2016;Zou and He 2018;Hoareau et al. 2019) more specialized and resource intensive studies, it might be worthwhile exploring the creation of a platform to document and collate promising results from such projects. Moreover, acknowledging the efforts of these young contributors, in a noteworthy manner, in research publications resulting from these leads would encourage more exploratory studies by students. ...
Article
Microbial fuel cells (MFCs) have shown immense potential as a one-stop solution for three major sustainability issues confronting the world today—energy security, global warming and wastewater management. MFCs represent a cross-disciplinary platform for research at the confluence of the natural and engineering sciences. The diversity of variables influencing performance of MFCs has garnered research interest across varied scientific disciplines since the beginning of this century. The increasing number of research publications has made it necessary to keep track of work being carried out by research groups across the globe and consolidate significant findings on a regular basis. Review articles are often the nodal points for beginners who are required to undertake an exploratory survey of literature to identify a suitable research problem. This ‘review of reviews’ is a ready-reckoner that directs readers to relevant reviews and research articles reporting significant developments in MFC research in the last two decades. The article also highlights the areas needing research attention which when addressed could take this technology a few more steps closer to practical implementation.
... These devices exploit electroactive biofilm growth on an anode to supply the energy in the form of electrical current required for thermodynamically unfavorable reactions that occur on the cathode through an external electron transfer. Depending on the species formed on the cathode, these systems comprise the microbial fuel cells (MFC), characterized by operating in a galvanic mode, and microbial electrolysis cells (MEC), which operate in an electrolytic mode to generate hydrogen gas as an energetic vector (Zou and He, 2018). ...
Article
Modeling and simulation of electrochemical reactors (ECRs) by computational fluid dynamics (CFD) techniques have been increasing during the last fifteen years. The need to improve the performance of existing electrolyzers or the development of new technologies has attracted the attention of the scientific community. Commercial and open-source codes are very valuable tools in pursuing such goals. ECRs studied by CFD simulations are those used in the following applications: electrosynthesis of chemicals and drugs, electrowinning of metals, chloralkali, redox flow batteries, and fuel cells. They also included those used in water treatment, such as electrocoagulation, electrochemical advanced oxidation processes, water disinfection, heavy metal ion removal, electro-deionization, and electrodialysis. In the context of the existing technologies, some ECRs have been improved through the characterization of the reaction environment, with some adaptations made inside the electrolyzers, such as accommodation of electrodes, use of plastic meshes acting as turbulence promoters, design of 3D printed electrodes, use of novel fluid distributors at the inlet of the cells, and optimization of the operational conditions such as flow rate, current density, the concentration of reactants and temperature. Several novel ECRs that have been built using CFD approaches for multiple fundamental studies and commercial applications are examined. Finally, an in-depth analysis of mathematical modeling scientific challenges in designing and assessing ECRs is presented.
... Bioelectrochemical systems (BESs) have recently appeared as an interesting technology for wastewater treatment and resource recovery. 5 The fundamentals of a BES are based on the activity of exoelectrogenic microorganisms that catalyse the electrochemical reactions that occur on the electrode surface of an electrochemical cell. These microorganisms have the ability to participate in electron transfer mechanisms to/from electrode surfaces, which are necessary for oxidation or reduction processes. ...
Article
BACKGROUND This work develops a simplified mathematical model to predict the performance of a bioelectrochemical system (BES), first working as a microbial fuel cell (MFC) and then as a microbial electrolysis cell (MEC), for the recovery of dissolved metals (Fe, Cu, Sn and Ni) from simulated industrial wastewater. Experimental data from a previous work were used as starting points for mathematical modelling. Wastewater was used as the catholyte and contained Cu²⁺ and Fe³⁺ (500 mg L‐1) and Sn²⁺ and Ni²⁺ (50 mg L‐1), while the anolyte was composed of sodium acetate. Two mixed microbial populations were considered in the anode compartment (electrogenic and non‐electrogenic biomass). Dissolved metal ions were the electron acceptors in the electrogenic mechanism: Cu²⁺ and Fe³⁺ under MFC mode and then Fe²⁺, Ni²⁺ and Sn²⁺ under MEC mode. RESULTS The model predicted the organic substrate and microbial biomass (anode chamber) and Fe³⁺ and Cu²⁺ (cathode chamber) concentrations during MFC operation. Monod kinetic and stoichiometric parameters were calibrated, and it was observed that most of the organic substrate underwent a non‐electrogenic mechanism. The generation of electric current until electron acceptors were removed was also predicted. Concentration profiles and first‐rate constant values for the decreased Sn²⁺, Ni²⁺ and Fe²⁺ concentrations during the subsequent MEC operation were also obtained. The model was then used for simulations under different experimental conditions. CONCLUSION This work offers a single grey‐box model proposal that is easy to implement, and it can be used as a practical tool for testing the removal of dissolved metals in BESs. This article is protected by copyright. All rights reserved.
Article
Microbial fuel cells (MFCs) and forward osmosis (FO) are both attractive and versatile wastewater treatment technologies that possess disadvantageous qualities that prevent their optimal performance. This study aimed to investigate how draw solute selection for FO treatment would affect MFC performance in a coupled FO‐MFC system. Two types of draw solutes, NH4HCO3 and NaCl were studied and it was found that 1.0 M NH4HCO3 (FO‐MFC‐A) and 0.68 M NaCl (FO‐MFC‐B) had similar water fluxes of 6.04 to 3.39 LMH and 6.25 to 3.54 LMH, respectively. The reverse salt flux from the draw decreased the feed solution resistance for both draw solutes but the FO‐MFC‐A system (0.32 W m‐2) had a higher maximum power density than the FO‐MFC‐B system (0.26 W m‐2). The current density for the FO‐MFC‐B system increased due to continuous solution resistance decrease while it remained constant for the FO‐MFC‐A. The difference in Coulombic efficiencies (32.8 % vs. 25.6 %) but similar Coulombic recoveries (10.2 % vs. 11.4%) between the FO‐MFC‐A and FO‐MFC‐B systems suggested that the FO‐MFC‐A might have the inhibited microbial activity by high ammonium/ammonia. The FO‐MFC‐A system had the lower energy consumption for nutrient removal (2.01 kWh kg‐1 NH4+‐N) and recovery (8.87 kWh kg‐1 NH4+‐N). These results have shown that NH4HCO3 as a draw solute can have advantages of higher power density, higher Coulombic efficiency, and recoverability for draw regeneration but its potential inhibition on microbial activity must also considered.
Chapter
The amount of waste produced each year is at an all-time high owing to high population expansion and urbanisation. Landfills have been and continue to be the most cost-effective waste disposal method. However, the environmental risks associated with leachate have caused surface and groundwater deterioration. As the leachate is hazardous, rich in organic, ammonia and metal elements, treating the liquid is energy-intensive and associated with costly procedures to fulfil current environmental laws. Microbial fuel cells (MFCs) could be the alternative method for leachate treatment. MFC is considered a promising and viable method because the device removes organic contaminants and generates bioelectricity during the oxidation process. This chapter investigates the robustness and effectiveness of the technology for removing carbon, nitrogen and phosphorus from landfill leachate and highlights and evaluates current developments in single and hybrid MFC. Recent advancements in combined MFC technology and their synergetic influence on boosting power densities, organic and nutrient removal and future difficulties were thoroughly explored. A sustainable strategy should be considered and designed for the MFC and its hybrid system to increase the success of the overall leachate treatment.KeywordsMicrobial fuel cellLandfill leachateWastewater treatmentEnergy recoveryOrganic carbon and ammonia removal
Article
Bioelectrochemical systems (BESs) are promising in self-sustaining energy recovery of wastewater. Cathode catalysts are crucial to enhancing the oxygen reduction reaction (ORR) process in BESs. In this study, a dual regulation strategy including solvent mediation and zinc fencing was proposed for regulation of catalyst spatial structure and active sites. The particle size of catalysts derived from bimetallic zeolitic imidazolate frameworks (ZIFs) was tuned over a wide range via solvent mediation while the dispersion of cobalt active sites was achieved via zinc fencing. As-optimized cobalt active sites embedded nitrogen-doped porous carbon with a Co/Zn atom ratio of 1/20 (Co1/20@NPC) directed a four-electron transfer pathway in ORR process. The BES employing Co1/20@NPC as cathode catalyst produced a maximum power density of 2057 ± 21 mW m⁻², 40% higher than the BES using Pt/C as cathode catalyst. Co1/20@NPC BES displayed fast organic elimination and efficient energy recovery with a coulombic efficiency of 73 ± 1% and a normalized energy recovery of 0.361 ± 0.006 kWh m⁻³. The outstanding ORR activity, high bioelectricity generation and long-term operation stability made Co1/20@NPC a prospective cathode catalyst. This dual regulation strategy provides implications for controllable synthesis of ZIF-derived catalysts with tailored structures and characteristics, and demonstrates potential in improving wastewater energy recovery performance in BESs.
Chapter
The excess availability of wastewater and reduction in the energy resources has initiated a new thought process of ‘waste to energy’. The green technology like solar and wind system utilises natural unending resources for production of valuable energy. To utilise waste as a source of energy we require process that a convert the chemical energy trapped in waste to green energy. The conventional technologies like anaerobic digestor produce methane, but the purity of product and time duration taken for the production makes the system unsustainable. The new bio-electrochemical system has been rectified as a potential process that can utilise waste, produce valuable products and is being optimised towards sustainability. This chapter presents a comparative review with respect to this new technology and its ability for resource recovery.
Article
Geobacter dominated electroactive biofilms (EABs) have been demonstrated to perform bidirectional extracel-lular electron transfer (EET) in bioelectrochemical systems, but it is largely unknown when nitrate is the electron acceptor at the cathode. If reverse EET occurs on biocathode, this EAB has to perform dissimilatory nitrate reduction to ammonia (DNRA) rather than denitrification according to genomes. Here, we have proven the feasibility of reverse bioelectron transfer in EAB, achieving a DNRA efficiency up to 93 ± 3% and high Faraday efficiency of 74 ± 1%. Constant current was found to be more effective than constant potential to maintain Geobacter on the cathode, which highly determines this electrotrophic respiration. The prevalent DNRA at constant current surpassed denitrification, demonstrated by the reverse tendencies of DNRA (nrfA) and deni-trification (nirS and nirK) gene transcription. Metatranscriptomics further revealed the possible electron uptake mechanisms by which the outer membrane (OmcZ and OmcB) and periplasmic cytochromes (PpcB and PpcD) may be involved. These findings extend our understanding of the bidirectional electron transfer and advance the applications of EABs.
Article
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This study explored the feasibility of treating wastewater using sulfur-driven autotrophic denitrification (SAD) coupled with the bio-cathode of microbial fuel cell (MFC), focusing on simultaneous bioelectricity generation, denitrification, and desulphurization. A maximum output voltage of 360 mV was obtained with a power generation cycle of 25 h when simulated wastewater with 100.0 mg/L of each -N and S2−-S was employed as the influent in the SAD-BMFC. Compared with solo SAD or MFC, SAD-BMFC obtained a higher -N removal rate (E12 h = 87.7%, E24 h = 100%), and less -N accumulation. S2−-S of the influent was almost completely removed, oxidized to S0-S (88.6–90.2 mg/L) and -S (9.8–11.4 mg/L). The reaction system achieved self-balance of acidity-alkalinity (pH 7.05–7.35). The SAD process was the main pathway for -N removal (80.2%) and a smaller proportion of electrons came from the bio-cathode. This study effectively combined SAD with a bio-cathode system for simultaneous energy harvest and bio-enhanced remediation of groundwater contaminated by both -N and S2−-S.
Article
Hydroponics is a modern cultivation technique that utilizes nutrient solutions instead of soil for crop production. Currently, challenges, such as high cost, high energy consumption, greenhouse gas emission, and significant wastewater generation are drawbacks that limit its scale up. On the other hand, bioelectrochemical systems have emerged as a sustainable technology that resolve some of the aforementioned drawbacks, albeit in other scenarios. Bioelectrochemical systems applications are well documented in desalination, metal recovery, energy generation, contamination remediation etc. This work conceptualizes the integration of bioelectrochemical systems and hydroponics with a view to improving the efficiency and sustainability of hydroponics. Firstly, a systematic review of the main challenges hindering hydroponic agriculture developments is first carried out to identify possible entry points for the proposed systems integration. Thereafter, a conceptualized point-by-point resolution of the main identified challenges of hydroponic systems through bioelectrochemical systems integration is explored. Furthermore, the feasibility, stability, and scalability of the conceptualized hydroponic-bioelectrochemical integrated systems are discussed.
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Over the centuries, humans have used medicinal plants to treat various diseases. Initially, these medications took the form of crude medications such as tinctures, teas, poultices, powders, and other herbal formulations. Almost 80% of the world population uses traditional medicines for primary health care, most of which involve the use of plant extracts. The study of plants continues, mainly, with the aim of discovering new secondary metabolites that can be used to recover health, both human and animal or vegetable. Cancer is a major public health problem worldwide and Mexico is not exempt from this problem. However, the great challenge for anticancer treatments is the specific release of the drug in the tumor tissue to avoid the adverse effects on normal cells. In this investigation, a species of the Buddleja genus is studied in terms of its cytotoxic activity in a prostate cancer cell line. Regarding the results found, it was obtained that the polar extract of aerial parts and the medium polarity extract of aerial parts have no cytotoxicity and high cytotoxicity, respectively against a prostate cancer cell line.
Chapter
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Various persistent organic pollutants (POPs) are increasingly being detected in numerous environmental matrices, including water. Even though there are currently some technologies for the elimination of these pollutants, it is necessary to evaluate their advantages, disadvantages, process time, and cost to find the optimal treatment depending on the characteristics of the pollutants and the matrix to remediate. This work was carried out to compare phase change technologies, advanced oxidation processes, and biological treatments for the elimination of POPs. In this chapter, a recent literature review of the aforementioned methods was performed. Studies are still being carried out to find the best way to eliminate POPs, as this depends on the treatment conditions, the type of water and the policies of each country, but biological treatments seem to be the best option so far.
Article
Although ammonia recovery from wastewater can be environmentally friendly and energy efficient compared to the conventional Haber-Bosch process, there is a lack of research on the reuse of the recovered ammonia to exhibit a complete picture of resource recovery. In this study, a microbial electrochemical system (MES) was used to recover ammonia from a mixture of anaerobic digester (AD) centrate and food wastewater at a volume ratio of 3:1. More than 60% of ammonia nitrogen was recovered with energy consumption of 2.7 kWh kg⁻¹ N. The catholyte of the MES, which contained the recovered ammonia, was used to prepare fertilizers to support the growth of a model plant Arabidopsis thaliana. It was observed that A. thaliana grown on the MES generated fertilizer amended with extra potassium, phosphorus, and trace elements showed comparable sizes and an even lower death rate (0%) than the control group (24%) that was added with a commercial fertilizer. RNA-Seq analyses were used to examine A. thaliana genetic responses to the MES generated fertilizers or the commercial counterpart. The comparative study offered metabolic insights into A. thaliana physiologies subject to the recovered nitrogen fertilizers. The results of this study have demonstrated the potential application of using the recovered ammonia from AD centrate as a nitrogen source in fertilizer and identified the necessity of supplementing other nutrient elements.
Article
Land application of livestock manure is a common waste utilization process that improves soil fertility and increases food production, while antibiotics in livestock manure posed potential threat to human and ecological health when applied to agricultural fields. Biological, thermochemical and bioelectrochemical technologies have been widely investigated to stabilize livestock manure and produce bioenergy. However, systematic information on the fates and conversion of antibiotics is still unclear. Therefore, this review first estimated the distribution of antibiotics in livestock manure. Additionally, the recent advances on the fates and degradation of antibiotics in livestock manure during the bioenergy production processes were summarized. Furthermore, the removal mechanisms of antibiotics by different treatment technologies, as well as their challenges and prospects were discussed. This review explored the research implications and proposed new avenues in the field of bioenergy conversion of livestock manure from a perspective of fates and conversion of antibiotics.
Article
Bioelectrochemical systems (BESs) with integrated photoactive components have been shown to be a promising strategy for enhancing the performance for bioenergy generation and pollutant removal. This study revealed an efficient photo-BES with an enhanced pollutant degradation rate by utilizing self-produced biomolecules as photosensitizers in situ. Results showed that the BES could increase the coulombic efficiency from 60.8 to 73.0% and the degradation rate of bisphenol A (BPA) from 0.030 to 0.189 h⁻¹ when the suspension in the reactor was illuminated with simulated sunlight in the absence of any external photosensitizers. We identified that the regular BES released many organic substances into the reactor during operation. These substances, including dissolved biomolecules and solid cell residues, were photoactive for producing hydroxyl radicals during light illumination. Quenching experiments verified that the •OH generated from the self-produced biophotosensitizers contributed to the enhanced degradation of BPA. Additionally, the phototransformation of biophotosensitizers was also observed in photo-BES. The quantity of tyrosine protein-like components decreased, but that of the humic components remained relatively stable. Our findings imply that BESs with integrated self-produced biophotosensitizers may be promising for constructing advanced electrochemical and biological systems for synchronous bioelectricity production and degradation of organic pollutants in wastewater treatments.
Chapter
Bioelectrochemical systems (BESs) have emerged as one innovative technology platter where different configurations of the experimental setup provide various applications, ranging from electricity generation, wastewater treatment, hydrogen and utility chemical production, bioremediation, desalination, etc. With growing interests in BESs, the number of mathematical modeling studies in this field has also grown. However, given the complex interdependence of the different processes, conventional deterministic models have so far achieved only moderate success. Considering the large number of unknowns in the system, data-based artificial intelligence (AI) methods, which do not require prior knowledge of the process, are now being used to study BES. This chapter presents a brief description and an overview of the different AI methods that have been used for predicting and controlling the performance of different types of BES.
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Microbial electrochemical system (MES) is considered a promising technology by the scientific community due to their greater potential of treating human wastes and animal urine along with the generation of electricity and recovery of resources with negative carbon footprints through anodic microbial catalytic reactions. Even with several challenges such as bio-electrochemical limitations, operating and fabrication costs, the MES has received attention due to the recent advancements in this field. The major issue of eutrophication in the wastewater occurred due to the phosphorus and nitrogen present in the urine source. Valuable byproducts can be recovered as the resource in the form of struvite as a valorization approach with substantial environmental benefits instead of removal through the conventional wastewater treatment systems. In this chapter, the scope, suitability, and challenges in the scale-up approach of utilizing human waste and animal urine for energy and resource recovery through microbial electrochemical systems are discussed. Even with several challenges such as bio-electrochemical limitations, operating and fabrication costs, the MES has drawn consideration due to the recent advancements in this field which may propel this technology to meet the demands in real-world applications.
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Greenhouse gases are the major cause of global warming. Carbon dioxide, a major greenhouse gas, is released into the atmosphere because of fossil fuel burning and deforestation. Researchers are trying to control escalating level of CO2 by a global approach of carbon capture, storage, and utilization (CCSU) methodology. Bioelectrochemical system (BES) is an assembly of electrochemical process with microbes for energy and valuable chemical generation, and waste biovalorization. BES application area includes desalinization of water, bioconversion of CO2 into chemicals and fuels, electricity production, electrobioremediation, production of hydrogen, and value-added chemical and fuel production. This chapter discusses the basics of BES technologies as well as in detail discusses MES (microbial electrosynthesis) a bioelectrochemical technology and its role in the reduction of CO2 to valuable products such as methanol, acetic acid, ethanol, hydrogen, butanol, hexanol, caproic acid, etc. However, this chapter also discusses various challenges hindering the upscaling of lab-scale MES into industrial level. Several strategies toward designing MES for better utilization of CO2 is discussed for a sustainable future of biorefinery.
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Diatoms are among the opaquest photosynthetic microorganism found in oceans, rivers, and freshwaters. They play a major role in reducing global warming as they fix more than 25% of atmospheric carbon di oxide (CO2). They are a reservoir of untapped potential with the multifaceted application including CO2 mitigation, play a vital role in the aquatic food web as primary producers, and wastewater remediation by quenching pollutants originating from diverse sources such as industries, agricultural, and human sources. Despite their abundance and diversity in nature, only a few species are currently used for biotechnological applications. Diatom biorefinery has gained importance in recent years as more and more algae are identified and explored as a source for lipids, pigments, and other biomolecules. In this chapter, the role of diatom biorefinery has been elaborated extensively displaying the potential of diatoms in carbon dioxide (CO2) mitigation, lipid production for biofuel, nutraceutical potential, and development of new-age drug molecules for therapeutic applications.
Article
Microbial electrosynthesis (MES) is capable of converting CO2 to CH4 using microorganisms as biocatalysts, but its performance is significantly restrained by the inherent weakness of naturally-grown biofilms, especially the low biomass loading on biocathodes. Here, we report a top-down biosynthetic approach to fabricate hybridized biofilms on biocathodes, and significantly enhance the methane production. In particular, microbes are captured and artificially loaded on the biocathode with the presence of graphene oxide (GO) and Fe3O4 nanoparticles. The aggregate of reduced graphene oxide (rGO), Fe3O4 and microbes brought in an initial high loading of microbes through magnetic assembling, resulting in a thick and dense biofilm on the rGO/Fe3O4 scaffold. The biocathode achieved an unprecedented CH4-producting rate of 605 ± 119 mmol/m²/d at −0.9 V vs. Ag/AgCl, which increased by 14.5-fold compared to the carbon cloth biocathode. This approach provides new opportunities for the development of high-performance electrochemically-active biofilms for MES, as well as other bioelectrochemical systems.
Article
Due to their numerous effects on human health and the natural environment, water contamination with heavy metals (HMs) and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of HMs-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of HMs from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes’ sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.
Article
Cultivating algae using wastewater nutrients is a potential approach to realize resource recovery that can contribute to circular economy. However, growing algae directly in a wastewater has problems such as bacterial contamination and a low biomass density. To address those problems, we investigated microalgal cultivation in a photobioreactor (PBR) fed with the nutrients extracted from wastewater by a microbial nutrient recovery cell (MNRC). With an external voltage of 0.3 V, the MNRC-PBR system removed 96% of COD and recovered 44% of NH4⁺-N and 39% of PO4³⁻-P at a hydraulic retention time of 7.2 hours. Microalgae cultivated in the nutrient recovery medium from the MNRC had 8.3-fold biomass density and 1.4-fold lipid contents, versus that cultivated in a food wastewater containing more nutrients. More significantly, 90% of biomass yielded from the MNRC-PBR system was microalgae, much higher than ∼30% in the food wastewater. A liquid exchange ratio of 30% achieved the highest microalgal density of 0.61 ± 0.06 g L⁻¹, comparable to that in a standard BG11 medium. There was a tradeoff between recycling PBR medium and microalgal growth. The accumulated salinity was observed in the extended operation of the MNRC-PBR system treating an actual food wastewater. The results of this study have demonstrated an effective approach to extract nutrients from wastewater for enhanced microalgal growth and improved biomass quality.
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Microbial electrosynthesis (MES) represents a sustainable platform that converts waste into resources, using microorganisms within an electrochemical cell. Traditionally, MES refers to the oxidation/reduction of a reactant at the electrode surface with externally applied potential bias. However, microbial fuel cells (MFCs) generate electrons that can drive electrochemical reactions at otherwise unbiased electrodes. Electrosynthesis in MFCs is driven by microbial oxidation of organic matter releasing electrons that force the migration of cationic species to the cathode. Here, we explore how electrosynthesis can coexist within electricity-producing MFCs thanks to electro-separation of cations, electroosmotic drag, and oxygen reduction within appropriately designed systems. More importantly, we report on a novel method of in situ modulation for electrosynthesis, through additional “pin” electrodes. Several MFC electrosynthesis modulating methods that adjust the electrode potential of each half-cell through the pin electrodes are presented. The innovative concept of electrosynthesis within the electricity producing MFCs provides a multidisciplinary platform converting waste-to-resources in a self-sustainable way.
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As people continue to study soil loss, remote sensing and GIS technology will also be widely used in soil loss estimation models. In the current research results, it is found that the factors of vegetation coverage can be obtained through remote sensing image data, such as vegetation index, soil utilization classification map, and the component image between soil and vegetation. GIS can store multi-source data, perform operational management, etc., from these perspectives, estimate soil loss, and make corresponding charts. For example, GIS can transform the weather station data into a continuous image through regression or interpolation to estimate the necessary precipitation when the soil is lost. Another essential factor in the soil loss model is soil. GIS can present the data in the form of a raster through soil sample data or a vector format map of soil types. To enrich the content of soil loss assessment, GIS has introduced DEM data, making terrain indicators quantified for better research. Scholars at home and abroad have done a lot of research and analysis on this algorithm, but in real life, the environment where the moving target is located is more complicated. Due to various interference factors, the accuracy of sports image detection and target tracking is difficult to determine. The current algorithm cannot accurately detect different changing scenes. For the sports image detection algorithm’s problems, this article combines the remote sensing image technology to study the mountain soil loss phenomenon and focuses on the sports image detection algorithm and remote sensing image technology, improving existing shortcomings in remote sensing image technology.
Chapter
Due to large quantity and containing rich resources (e.g., chemical energy, metals, fresh water and nutrients), recovery resources from municipal and industrial wastewaters can be considered where resource recovery economies can be applied. Simultaneously, resource recovery during wastewater treatment will make treatment processes more economically viable and compliant to increasingly tight environmental regulations. Bioelectrochemical systems (BESs) have emerged as a platform technology to recover resources from wastewater treatment. In this chapter, a comprehensive and critical review of resource recovery via BES from wastewater is conducted. The basic information of BES as well as the processes of resource recovery through BES at the laboratory and plant scale is introduced. Furthermore, the current challenges related to the BES applications for resource recovery and the possible development directions are discussed.
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Hydrogen gas is a green energy carrier with great environmental benefits. Microbial electrolysis cells (MECs) can convert low-grade organic matter to hydrogen gas with low energy consumption and have gained a growing interest in the past decade. Cathode catalysts for the hydrogen evolution reaction (HER) present a major challenge for the development and future applications of MECs. An ideal cathode catalyst should be catalytically active, simple to synthesize, durable in a complex environment, and cost-effective. A variety of noble-metal free catalysts have been developed and investigated for HER in MECs, including Nickel and its alloys, MoS2 , carbon-based catalysts and biocatalysts. MECs in turn can serve as a research platform to study the durability of the HER catalysts. This personal account has reviewed, analyzed, and discussed those catalysts with an emphasis on synthesis and modification, system performance and potential for practical applications. It is expected to provide insights into the development of HER catalysts towards MEC applications.
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Zero liquid discharge (ZLD) — a wastewater management strategy that eliminates liquid waste and maximizes water usage efficiency — has attracted renewed interest worldwide in recent years. Although implementation of ZLD reduces water pollution and augments water supply, the technology is constrained by high cost and intensive energy consumption. In this critical review, we discuss the drivers, incentives, technologies, and environmental impacts of ZLD. Within this framework, the global applications of ZLD in the United States and emerging economies such as China and India are examined. We highlight the evolution of ZLD from thermal- to membrane-based processes, and analyze the advantages and limitations of existing and emerging ZLD technologies. The potential environmental impacts of ZLD, notably greenhouse gas emission and generation of solid waste, are discussed and the prospects of ZLD technologies and research needs are highlighted.
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We report an integrated experimental and simulation study of ammonia recovery using microbial electrolysis cells (MECs). The transport of various species during the batch-mode operation of an MEC was examined experimentally and the results were used to validate the mathematical model for such an operation. It was found that, while the generated electrical current through the system tends to acidify (or basify) the anolyte (or catholyte), their effects are buffered by a cascade of chemical groups such as the NH3/NH4+ group, leading to relatively stable pH values in both anolyte and catholyte. The transport of NH4+ ions accounts for ~90% of the total current, thus quantitatively confirming that the NH4+ ions serve as effective proton shuttles during MEC operations. Analysis further indicated that, because of the Donnan equilibrium at cation exchange membrane-anolyte/catholyte interfaces, the Na+ ion in the anolyte actually facilitates the transport of NH4+ ions during the early stage of a batch cycle and they compete with the NH4+ ions weakly at later time. These insights, along with a new and simple method for predicting the strength of ammonia diffusion from the catholyte toward the anolyte, will help effective design and operation of bioeletrochemical system-based ammonia recovery systems.
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The enhancement of microbial electrosynthesis (MES) of acetate from CO2 to performance levels that could potentially support practical implementations of the technology must go through the optimization of key design and operating conditions. We report that higher proton availability drastically increases the acetate production rate with pH 5.2 found to be optimal, which will likely suppress methanogenic activity without inhibitor addition. Applied cathode potential as low as 1.1 V vs. SHE still achieved 99% of electron recovery in the form of acetate at a current density of around -200 A m 2. These current densities are leading to an exceptional acetate production rate of up to 1330 g m-2 day-1 at pH 6.7. Using highly open macroporous reticulated vitreous carbon electrodes with macropore sizes of about 0.6 mm diameter was found to be optimal to achieve a good balance between total surface area available for biofilm formation and effective mass transfer between the bulk liquid and the electrode/biofilm surface. Furthermore, we also successfully demonstrated the use of a synthetic biogas mixture as carbon dioxide source, yielding similarly high MES performance as pure CO2. This would allow this process to be used effectively for both biogas quality improvement and conversion of the available CO2 to acetate.
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Energy self-sufficiency is a highly desirable goal of sustainable wastewater treatment. Herein, a combined system of a microbial fuel cell and an intermittently aerated biological filter (MFC-IABF) was designed and operated in an energy self-sufficient manner. The system was fed with synthetic wastewater (COD = 1000 mg L(-1)) in continuous mode for more than 3 months at room temperature (~25 °C). Voltage output was increased to 5 ± 0.4 V using a capacitor-based circuit. The MFC produced electricity to power the pumping and aeration systems in IABF, concomitantly removing COD. The IABF operating under an intermittent aeration mode (aeration rate 1000 ± 80 mL h(-1)) removed the residual nutrients and improved the water quality at HRT = 7.2 h. This two-stage combined system obtained 93.9% SCOD removal and 91.7% TCOD removal (effluent SCOD = 61 mg L(-1), TCOD = 82.8 mg L(-1)). Energy analysis indicated that the MFC unit produced sufficient energy (0.27 kWh m(-3)) to support the pumping system (0.014 kWh m(-3)) and aeration system (0.22 kWh m(-3)). These results demonstrated that the combined MFC-IABF system could be operated in an energy self-sufficient manner, resulting to high-quality effluent.
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High product specificity and production rate are regarded as key success parameters for large-scale applicability of a (bio)chemical reaction technology. Here we report a significant performance enhancement in acetate formation from CO2, reaching comparable productivity levels as in industrial fermentation processes (volumetric production rate and product yield). A biocathode current density of -102 ± 1 A m 2 and acetic acid production rate of 685 ± 30 g m-2 day 1 have been achieved in this study. High recoveries of 94 ± 2% of the CO2 supplied as sole carbon source and 100 ± 4 % of electrons into the final product (acetic acid) were achieved after development of a mature biofilm, reaching an elevated product titer of up to 11 g L-1. This high product specificity is remarkable for mixed microbial cultures, which would make the product downstream processing easier and the technology more attractive. This performance enhancement was enabled through the combination of a well acclimatized and enriched microbial culture (very fast start up after culture transfer), coupled with the use of a newly synthesized electrode material, EPD-3D. The throwing power of the electrophoretic deposition technique, method suitable for large-scale production, was harnessed to form multi-walled carbon nanotubes coatings onto reticulated vitreous carbon to generate a hierarchical porous structure.
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Using carbon dioxide for bioproduction combines decreased greenhouse gas emissions with a decreased dependence on fossil carbon for production of multicarbon products. Microbial electrosynthesis (MES) enables this, using renewable energy to drive the reduction of CO2 at the cathode of an electrochemical cell. To date, low product concentrations preclude cost-effective extraction during MES. Here we present an approach that couples production and recovery of acetate in a single, three-chamber reactor system. Acetate was produced at 61% Coulombic efficiency and fully recovered as an acidified stream containing up to 13.5 g L −1 (225 mM) acetic acid, the highest obtained thus far. In contrast to previous MES studies, a single separated acidic product was generated through in situ membrane electrolysis enabling further upgrading.
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Microbial electrochemistry is the study and application of interactions between living microbial cells and electrodes (i.e. electron conductors, capacitive materials). For a long time this subfield of bioelectrochemistry has been the interest of mainly fundamental researchers. This has considerably changed during the last decade and microbial electrochemistry gained interest from applied researchers and engineers. These researchers took the microbial fuel cell (MFC), which is a system that converts the chemical energy of organic material in wastewater into electric power, from a concept to a technology. In addition, a plethora of derivative technologies, such as microbial electrolysis cells (MECs), microbial desalination cells (MDCs), photomicrobial fuel cells (photoMFCs), microbial electrosynthesis (MES), and biocomputing have been developed. The growing number of systems is often referred to in literature under the termini bioelectrochemical system (BES), microbial electrochemical technology (MET), or electrobiotechnology. Within this article we introduce a classification of technologies based on interfacing microbiology and electrochemistry. We argue that BESs comprise all systems based on bioelectrochemistry, with a further layer of termini through the use of METs. Primary METs are based on extracellular electron transfer (direct or mediated), whereas secondary METs include systems in which electrochemistry is connected – at least through ionic contact – with a microbial process via the electrochemical control or adaptation of environmental parameters, such as pH or metabolite concentration level.
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The microbial desalination cell (MDC) is a newly-developed technology which integrates the microbial fuel cell (MFC) process and electrodialysis for wastewater treatment, water desalination and production of renewable energy. Due to free energy requirements and environmentally friendly technologies, MDC recently received considerable attention for desalination and wastewater treatment. The technology can either be used as a stand-alone process, or can be combined with other desalination processes, such as reverse osmosis (RO) or electrodialysis. Recently, several different modifications of MDCs have been developed including stacked MDCs, biocathode MDCs and recirculation MDCs.
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We report on a novel biocompatible, highly conductive three-dimensional cathode manufactured by direct growth of flexible multiwalled carbon nanotubes on reticulated vitreous carbon (NanoWeb-RVC) for the improvement of microbial bioelectrosynthesis (MES). NanoWeb-RVC allows for an enhanced bacterial attachment and biofilm development within its hierarchical porous structure. 1.7 and 2.6 fold higher current density and acetate bioproduction rate normalized to total surface area were reached on NanoWeb-RVC versus a carbon plate control for the microbial reduction of carbon dioxide by mixed cultures. This is the first study showing better intrinsic efficiency as biocathode material of a three-dimensional electrode versus a flat electrode: this comparison has been made considering the total surface area of the porous electrode, and not just the projected surface area. Therefore, the improved performance is attributed to the nanostructure of the electrode and not to an increase in surface area. Unmodified r
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To process large volumes of wastewater, microbial fuel cells (MFCs) would require anodophilic bacteria preferably operating at high flow-rates. The effect of flow-rate on different microbial consortia was examined during anodic biofilm development, using inocula designed to enrich either aerobes/facultative species or anaerobes. All MFCs underperformed at high flow-rates in the early stages, however, the aerobic type – following anodic biofilm development – subsequently exhibited more marked improvement. Scanning electron microscopy showed some variation in biofilm formation where clumpy growth was associated with lower power. Over time both power and internal resistance increased for the low flow-rates perhaps explained by an evolving microflora that consequently changed redox potential. An overshoot was observed in power curves, which was attributed to increased internal resistance due to ionic depletion and/or microbial exhaustion. To the best of the authors’ knowledge this is the first time that such phenomena are explained from the internal resistance perspective.
Book
Volume 9: Advanced Biological Treatment Processes in the Handbook of Environmental Engineering series provides critical insight into pollution-abatement engineering. This outstanding collection of methodologies is designed as a review of engineering systems currently being used, as well as their potential for use in pollution abatement. The book’s expert panel of authors provides a look at a range of topics, including principles and kinetics of biological processes, vertical shaft bioreactors, upflow sludge blanket filtration, membrane bioreactors, column bioreactor, SBR, nitrification, denitrification, and emerging biological processes. Volume 9: Advanced Biological Treatment Processes and its sister book - Volume 8: Biological Treatment Processes – are indispensable as both basic biological treatment textbooks and comprehensive reference books for advanced undergraduate and graduate students, designers of waste treatment systems, scientists, and researchers. A gold-standard addition to The Humana Press series, Volume 9: Advanced Biological Treatment Processes gives readers a cutting-edge illustration of the theory and practice of biological abatement systems and their critical role in environmental issues today.
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Bioelectrochemical systems (BES) can recover ammonia from wastewater driven by electricity generation. However, energy consumption of such an approach has not been well evaluated. In this study, the effects of several key operating factors including catholyte aeration rate, external voltage, and external resistance on both ammonia recovery and energy consumption were systematically investigated. A mathematical model developed for ammonia removal/recovery in BES was applied to help interpret the experimental results. It was found that a high aeration rate in the catholyte could facilitate ammonia recovery. An aeration rate of 100 mL min⁻¹ resulted in the lowest energy consumption of 4.9 kWh kg⁻¹ N recovery among the tested aeration rates. A low external resistance facilitated the ammonia recovery via higher current generation, while a moderate external voltage (e.g., 0.5 V) helped to achieve low energy consumption. The highest ammonia recovery rate of 7.1 g N m⁻² d⁻¹ was obtained with energy consumption of 5.7 kWh kg⁻¹ N recovery. Therefore, there is a trade-off between energy consumption and ammonia recovery.
Article
Recovering valuable resources from wastewater will transform wastewater management from a treatment focused to sustainability focused strategy, and creates the need for new technology development. An innovative treatment concept - osmotic bioelectrochemical system (OsBES), which is based on cooperation between bioelectrochemical systems (BES) and forward osmosis (FO), has been introduced and studied in the past few years. An OsBES can accomplish simultaneous treatment of wastewater and recovery of resources such as nutrient, energy, and water (NEW). The cooperation can be accomplished in either an internal (integrated OsBES) or external (coupled OsBES) configuration, through a strong synergy between BES and FO. BES can provide draw solute, perform pre-treatment, or reduce reverse salt flux to help with FO operation; while FO can achieve water recovery, enhance current generation, and supply energy sources to BES operation. Given much progress and interest in the OsBES, this paper has reviewed the past studies, described the current status, presented qualitative and quantitative analyses, and discussed the perspectives of the OsBES technology with a focus on NEW recovery from wastewater. The challenges for further researching and developing OsBES have also been identified.
Article
The production of hierarchical hybrid conductive materials that are mesoporous, with pores spanning from sub-micron to microns in size, is important for large-area electrode applications. Here, a simple one-step, low-cost method to fabricate a metal oxide-carbon hybrid materials with a hierarchical pore structure in a microwave oven is demonstrated. Microwave pyrolysis of ferrocene using carbon felt as a microwave absorber, a method that is rapid (tens of seconds), does not require harsh conditions nor costly equipment is utilized, and can be readily scaled up. The produced material has a high specific surface area, a multi-length scale porous structure and a high conductivity, and is quite stable, making it promising for many practical applications. As an electrode in microbial electrosynthesis, the performance is improved by a factor of five and an optimal biofilm of the microorganism is formed on the surface.
Article
Recovery of nutrients, water, and energy from high-strength sidestream centrate offers benefits such as reusable resource, minimized discharge and cost-savings in mainstream treatment. Herein, a microbial electrolysis cell - forward osmosis (MEC-FO) hybrid system has been investigated for integrated nutrient-energy-water (NEW) recovery with emphasis on quantified mass balance and energy evaluation. In a closed-loop mode, the hybrid system achieved recovery of 54.2 ± 1.9% of water (70.4 ± 2.4 mL), 99.7 ± 13.0% of net ammonium nitrogen (8.99 ± 0.75 mmol, with extended N2 stripping), and 79.5 ± 0.5% of phosphorus (as struvite, 0.16 ± 0.01 mmol). Ammonium loss primarily from reverse solute flux was fully compensated by the reclaimed ammonium under 6-h extended N2 stripping to achieve self-sustained FO process. The generated hydrogen gas could potentially cover up to 28.7 ± 1.5% of total energy input, rendering a specific energy consumption rate of 1.73 ± 0.08 kWh m−3 treated centrate, 0.57 ± 0.04 kWh kg−1 COD, 1.10 ± 0.05 kWh kg−1 removed NH4+-N, 1.17 ± 0.06 kWh kg−1 recovered NH4+-N, or 5.75 ± 0.54 kWh kg−1 struvite. Recycling of excess Mg2+ reduced its dosage to 0.08 kg Mg2+/kg struvite. These results have demonstrated the successful synergy between MEC and FO to achieve multi-resource recovery, and encouraged further investigation to address the challenges such as enhanced hydrogen production, reducing nutrient loss, and optimizing MEC-FO coordination towards an energy-efficient NEW recovery process.
Article
Bioelectrochemical reduction of carbon dioxide (CO2) to multi-carbon organic compounds particularly acetate has been achieved in microbial electrosynthesis (MES) using the reducing equivalents produced at the electrically polarized cathode. MES based on CO2 reduction produced 7–10 g L⁻¹ acetate at the cathode while operating the CO2 fed reactor in batch mode using the homoacetogenic activity enriched mixed culture. An integration of acetate extraction from the catholyte is interesting, firstly to recover the product and secondly to reduce the probable product inhibition due to the accumulation of fatty acids. We investigated acetate production from CO2 in MES in combination with a batch-wise removal of acetate from the broth using a commercially available anion-exchange resin (Amberlite™ FPA53). Acetate sorptions of 10–20 mg g⁻¹ resin were observed from the catholyte broth. The production of acetate from CO2 continued at 0.5 g L⁻¹ d⁻¹ after the acetate removal by sorption. Overall, an MES system for the production and separation of acetate from CO2 was technically feasible through the integration of MES with an anion exchange resin.
Article
Spirulina was cultivated in cathodic compartments of photo-microbial fuel cells (P-MFC). Anodic compartments were fed with swine-farming wastewater, enriched with sodium acetate (2.4 gCOD L-1). Photosynthetic oxygen generation rates were sufficient to sustain cathodic oxygen reduction, significantly improving P-MFC electrochemical performances, as compared to water-cathode control experiments. Power densities (0.8 – 1 W m-2) approached those of air-cathode MFCs, run as control. COD was efficiently removed and only negligible fractions leaked to the cathodic chamber. Spirulina growth rates were comparable to those of control (MFC-free) cultures, while pH was significantly (0.5 - 1 unit) higher in P-MFCs, due to cathodic reactions. Alkaliphilic photosynthetic microrganisms like Spirulina might take advantage of these selective conditions. Electro-migration along with diffusion to the cathodic compartment concurred for the recovery of most nutrients. Only P and Mg were retained in the anodic chamber. A deeper look into electro-osmotic mechanisms should be addressed in future studies.
Article
Forward osmosis (FO) has been widely studied for desalination or water recovery from wastewater, and one of its key challenges for practical applications is reverse solute flux (RSF). RSF can cause loss of draw solutes, salinity build-up and undesired contamination at the feed side. In this study, in-situ electrolysis was employed to mitigate RSF in a three-chamber FO system (“e-FO”) with Na2SO4 as a draw solute and deionized (DI) water as a feed. Operation parameters including applied voltage, membrane orientation and initial draw concentrations were systematically investigated to optimize the e-FO performance and reduce RSF. Applying a voltage of 1.5 V achieved a RSF of 6.78 ± 0.55 mmol m−2 h−1 and a specific RSF of 0.138 ± 0.011 g L−1 in the FO mode and with 1 M Na2SO4 as the draw, rendering ∼57% reduction of solute leakage compared to the control without the applied voltage. The reduced RSF should be attributed to constrained ion migration induced by the coactions of electric dragging force (≥1.5 V) and high solute rejection of the FO membrane. Reducing the intensity of the solution recirculation from 60 to 10 mL min−1 significantly reduced specific energy consumption of the e-FO system from 0.693 ± 0.127 to 0.022 ± 0.004 kWh m−3 extracted water or from 1.103 ± 0.059 to 0.044 ± 0.002 kWh kg−1 reduced reversed solute. These results have demonstrated that the electrolysis-assisted RSF mitigation could be an energy-efficient method for controlling RSF towards sustainable FO applications.
Article
Sporomusa ovata DSM-2662 produces high rate of acetate during microbial electrosynthesis (MES) by reducing CO2 with electrons coming from a cathode. Here, we investigated other Sporomusa for MES with cathode potential set at -690 mV vs SHE to establish if this capacity is conserved among this genus and to identify more performant strains. S. ovata DSM-2663 produced acetate 1.8 fold faster than S. ovata DSM-2662. On the contrary, S. ovata DSM-3300 was 2.7 fold slower whereas Sporomusa aerivorans had no MES activity. These results indicate that MES performance varies among Sporomusa. During MES, electron transfer from cathode to microbes often occurs via H2. To establish if efficient coupling between H2 oxidation and CO2 reduction may explain why specific acetogens are more productive MES catalysts, the metabolisms of the investigated Sporomusa were characterized under H2:CO2. Results suggest that other phenotypic traits besides the capacity to oxidize H2 efficiently are involved.
Article
Mathematical modeling is an important tool to investigate the performance of microbial fuel cell (MFC) towards its optimized design. To overcome the shortcoming of traditional MFC models, an ensemble model is developed through integrating both engineering model and statistical analytics for the extrapolation scenarios in this study. Such an ensemble model can reduce laboring effort in parameter calibration and require fewer measurement data to achieve comparable accuracy to traditional statistical model under both the normal and extreme operation regions. Based on different weight between current generation and organic removal efficiency, the ensemble model can give recommended input factor settings to achieve the best current generation and organic removal efficiency. The model predicts a set of optimal design factors for the present tubular MFCs including the anode flow rate of 3.47 mL min⁻¹, organic concentration of 0.71 g L⁻¹, and catholyte pumping flow rate of 14.74 mL min⁻¹ to achieve the peak current at 39.2 mA. To maintain 100% organic removal efficiency, the anode flow rate and organic concentration should be controlled lower than 1.04 mL min⁻¹ and 0.22 g L⁻¹, respectively. The developed ensemble model can be potentially modified to model other types of MFCs or bioelectrochemical systems.